It is now common for a commercial aircraft to be equipped with a flight guidance and management system (FGMS), which includes a flight management system (FMS) and a flight guidance system (FGS) having an autopilot functionality. The FMS of a modern FGMS is often capable of operating in a precision approach mode, such as an “instrument landing system” or “ILS” mode, when both lateral (localizer) and vertical (glideslope) guidance is available. Vertical guidance, in particular, may be provided by a glideslope (G/S) antenna array, which is located near the runway touchdown zone and which broadcasts a G/S signal over a selected channel. Certain antennae in the array modulate a first component of the G/S at a first frequency (e.g., 90 hertz), while other antennae in the array modulate a second component of the G/S signal at a second frequency (e.g., 150 hertz). Collectively, the components of the G/S signal define a G/S beam, which originates from an anchor point at the runway's threshold and projects through the final approach fix. When in range of the G/S antenna array, the G/S signal is received by, for example, a multi-mode receiver deployed onboard the aircraft. The G/S signal permits the FGS autopilot to determine the location of the G/S beam and the aircraft's position relative thereto. The aircraft, whether controlled directly by the FGS autopilot or by the pilot utilizing visual queues provided on the primary flight display (PFD), can then be guided vertically along the G/S beam to ensure a safe and accurate landing.
When unable to operate in a precision approach mode due to, for example, lack of a G/S signal, the FMS may operate in a non-precision approach mode. In one known non-precision approach mode commonly referred to as a “flight management (FM) vertical guidance mode,” the FMS utilizes data from available navigational aids (e.g., Air Data Computers, Inertial Reference Systems, non-directional beacons, global positioning systems, localizers, very high frequency omni-directional radio devices, and the like) to provide vertical guidance by continually calculating a target trajectory during a particular approach. Although compatible with virtually all approach types, including non-linear or curved approaches, the FM vertical guidance mode generally does not provide the same precision guidance capabilities and intuitive pilot controls as does the ILS mode described above. Thus, in an effort to replace the FM vertical guidance mode, a new non-precision approach mode (referred to herein as “an FMS landing system (FLS) approach mode”) has been recently been developed and implemented that mimics the precision ILS approach mode. When the FMS is operating in the FLS guidance mode, the FGS autopilot utilizes data derived from systems onboard the aircraft to construct a virtual model of a G/S beam. The FMS, in conjunction with the FGS and other onboard systems, may then generate visual queues on the PFD or other cockpit display, which the pilot may utilize to vertically guide the aircraft to the runway in essentially the same manner as during an ILS approach.
Although providing a highly useful ILS-like functionality, the FLS guidance mode may be incompatible with certain approaches. For example, due to the manner in which the virtual G/S beam is modeled, the FLS guidance mode is generally incompatible with curved (e.g., S-shaped) approaches. In addition, the FLS guidance mode may be incompatible with approaches having low required navigational performance (RNP) values or approaches requiring adherence to RNP authorization required (AR) protocols. However, within a conventional flight management system, the FLS functionality is either wholly enabled or disabled within a configurable and separately-loadable flight manager Operational Program Configuration (OPC) software database or via a set of input configuration parameters; thus, after being activated during initial software configuration, the FLS guidance mode cannot be deactivated by a pilot or other member of the aircrew. Consequently, in instances wherein the FLS guidance mode cannot be utilized during a selected approach, the pilot may be forced to request and fly a new approach, which can add unnecessary delay and cost to the flight procedure. Alternatively, the pilot may be forced to fly the selected approach using a manual mode of operation (e.g., through manual selection of the Flight Path Angle target or selection of the Vertical Speed target).
There thus exists an ongoing need to provide embodiments of a flight management system, a process, and a program product that enable a pilot to dynamically switch between a FLS guidance mode and an FM vertical guidance approach mode after selection of a non-precision approach within a flight plan. Other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.